1. Field of the Invention
The present invention relates to a single-crystal nitride-based semiconductor substrate and a method of manufacturing a vertical type nitride-based light emitting device by using the same. More particularly, the present invention relates to a method of growing a single-crystal nitride-based semiconductor substrate under high temperature and hydrogen atmosphere by using a seed material layer (“SML”) and a multifunctional substrate (“MS”), which are sequentially formed on an upper surface of a first substrate (“FS”) so as to prevent mechanical and thermal strain and decomposition from occurring at the upper surface of the first substrate including sapphire, silicon (Si), zinc oxide (“ZnO”) or gallium arsenide (“GaAs”). The present invention also relates to a high-quality nitride-based light emitting device and a manufacturing method thereof, in which the nitride-based light emitting device employs a single-crystal nitride-based semiconductor substrate and a light emitting structure, so that the nitride-based light emitting device has a large size and represents superior light efficiency and heat dissipation while being operated at a low operational voltage.
2. Description of the Related Art
With the rapid technological advance of optoelectronic devices, such as blue/green diodes, (near) infrared light emitting diodes, laser diodes and optical sensors, single-crystal nitride-based semiconductors have become very important materials in optical industrial fields. In general, optoelectronic devices employing the single-crystal nitride-based semiconductors are grown from the upper surface of a thick insulating sapphire substrate or a conductive silicon carbide (“SiC”) substrate under the hydrogen atmosphere where ammonium (“NH3”) and hydrogen (“H2”) carrier gas are provided in a high temperature condition of 1200° C. or more. However, since the insulating sapphire substrate or the conductive silicon carbide substrate is expensive as compared with a silicon substrate, the insulating sapphire substrate and the conductive silicon carbide substrate are inefficient for cost purposes. Since the nitride-based optoelectronic devices generate a large amount of heat during the operation thereof, the substrate must dissipate the heat generated from the nitride-based optoelectronic devices. However, if the nitride-based optoelectronic devices are formed on the upper surface of the insulating sapphire substrate having a thickness of 70 micron meters or more, the insulating sapphire substrate cannot easily dissipate the heat because the insulating sapphire substrate has inferior thermal conductivity. Therefore, the insulating sapphire substrate may not serve as a next-generation white light source.
Different from the thick insulating sapphire substrate and the silicon carbide substrate, a transparent conductive zinc oxide (“ZnO”) substrate has a small difference in a lattice constant relative to the nitride-based semiconductor while representing superior electrical and thermal conductivities and higher light transmittance. In addition, the transparent ZnO substrate can be fabricated at an inexpensive cost. Therefore, the transparent ZnO substrate has been recently spotlighted as a next-generation substrate for the nitride-based light emitting devices. However, the surface of the transparent conductive zinc oxide (“ZnO”) substrate becomes unstable under a high temperature of 600° C. or more and a high vacuum of 10−3 torr or more, thus easily decomposing the materials of the transparent conductive zinc oxide (ZnO) substrate. In addition, reduction of the transparent conductive ZnO substrate is promoted in reducing ambient employment of ammonium (“NH3”) and hydrogen (“H2”). For this reason, the single-crystal nitride-based semiconductor is rarely grown under the reducing ambient having a temperature of 800° C. or more.
Other conductive substrates, including silicon (Si), silicon germanium (“SiGe”), or gallium arsenide (“GaAs”), have been suggested. However, these conductive substrates also represent problems at a temperature of 500° C. or more due to the motion of the dislocation slip system provided in the conductive substrates, thereby causing strain to and decomposition of materials. In addition, since these conductive substrates represent large differences in lattice constant and thermal expansion coefficient relative to the nitride-based semiconductor, high-quality nitride-based layers may not be easily grown from the above conductive substrates.
A laser lift off (“LLO”) method has been most recently spotlighted in the industrial field as a method of manufacturing a nitride-based light emitting device for a next-generation high-brightness white light source. According to the LLO method, a high-quality nitride-based semiconductor layer or a light emitting structure is grown from an upper surface of a sapphire substrate having inferior thermal and electrical conductivities, and then a strong energy laser beam is irradiated onto a rear surface of the sapphire substrate, thereby separating the nitride semiconductor layer and the light emitting structure from the sapphire substrate. A highly reliable nitride-based light emitting device representing high brightness and having a large size required for the next-generation white light source can be manufactured by using the LLO method. However, since a strong energy laser beam is applied to the sapphire substrate in order to separate the nitride-based semiconductor layer and the light emitting structure from the sapphire substrate, heat having a temperature of 900° C. or more is generated from the interfacial surface between the sapphire substrate and the nitride-based semiconductor layer/the light emitting structure, so that the nitride-based semiconductor layer may be damaged or deformed, lowering the product yield and causing difficulties during the manufacturing process.